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Physiologic Changes in

Pregnancy

Thomas S. Ivester, MD, MPH

Maternal-Fetal Medicine

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Why should this matter to me???

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Relevance of OB physiology

5-10 % of women in ER are pregnant

Many dont know or show

Any female of reproductive age could be

pregnant

Should be assumed so!

Virtually every organ system affected

Can touch almost any specialty

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Case history

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Case 1

36 y.o. female presents to ER

CC: Fatigue, dyspnea, chest pain

HPI: Progressive SOB and dyspnea over several weeks.

Poor exercise tolerance and easy fatigability

get winded after 1 flight of stairs

Substernal chest pain, peaks in morning and night Nocturnal cough, semi-productiveclear

Leg swelling

polyuria

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Case 1

PMH

Mild obesity

Ob/gynmenses at age 12; irregular menses; nopregnancies

Meds

Oral contraceptives

multivitamins Social

Married for 2 years. No exposures

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Case 1: PE

Skin

warm, clammy. Mild facial acne and increased hairmedium coarseness

HEENT

NC/AT. Nasal mucosa slightly hyperemic.

Mild non-nodular thyromegaly

CV Tachycardia (HR 107)

+ JVD

2/6 systolic murmurs over pulmonic and aortic v.

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PE contd

Chest

Clear bilaterally. Diaphragm elevated with decreased

excursion Ext

1+ pretibial pitting edema

Abd

Skinspider angiomata and striae. Medium course

hair, infraumbilical.

Distended, firm, non-tender.

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Studies / labs

EKG:

Sinus rhythm; tachy; Left axis deviation

CXR: Lungs clear. Cardiomegaly. Increased vascular

markings

Labs:

Hct 32% (low); WBC 12 (high) Cholesterol 300 mg/dl

D-dimer elevated

Potassium and creatinine low

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What does she have???

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General Principles

Most changes begin early

Even before pregnancy recognized

Most are hormonally driven Progesterone, estrogen, renin / aldosterone, cortisol,

insulin

Some mechanically driven

Designed to optimize conditions for fetus &

prepare for delivery

Delivery of oxygen & nutrients

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Cardiovascular & Hematologic

Vascular

Decreased tone / vaso-relaxation

SVR decreased 20% Positional effects

Placentalow resistance shunt

Hematologic

Blood volume increases 50-100%

RBC increases 25-40%

Relative anemia (physiologic)

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Hematologic

Hypercoagulable

Estrogen & Vascular stasis

Increased risk for thromboembolic disease

Increase in fibrinogen, all coag factors except II, V,

XII

Fall in protein S and sensitivity to APC

Fall in platelets and factor XI and XIII

Increase in WBC

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Changes in the Pump

Cardiac axis displaced cephalad and left

PMI lateral & elevated (not just due to baby!) Altered thoracic dimensions

Left axis deviation

Murmurs > 96%

Virtually all valves Esp. Aortic and Pulmonary

Mammary Souffle

Rateincreased (80s typical)

Ventricular distention25% increase

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More changes in the Pump

Rhythm

Non-specific ST & T changes

Increase in dysrhythmias Physiologic hypokalemia

Anatomy

LVH & Pericardial effusion

Function

Increased & markedly fluctuating output

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Blood Pressure

50

55

60

65

70

75

8 to 16 20 to 25 28 to 35 36 to 40

Normal

Normal

Weeks

(Benedetto et al, Obstet Gynecol, 1996)

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Pregnancy Adaptations

Factor Preg. NonPrg Change

CO 6.2 4.3 +43%

MAP 86 90 -10%

SVR 1210 1530 -21%

PVR 78 119 -34%

HR 83 71 +17%

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Anatomical considerations

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Uterine Position over Time

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Cardiac OutputPositional

Effects Aorto-caval Compression

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Labor Changes

SVRIncreased 10-25% with CTX

Volumeautotransfusion 300-500cc

Cardiac output -8cm Increased 34%

Changes over pregnancy baseline CO.

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The Fetus and Placenta

Fetus (akathe parasite)

A sensitive survivor

A window Placenta

A veritable hormone factory

Receives 20-25% of cardiac output*

750-1000 ml/min

Refractory to vasoactive meds

Uses as much O2 as fetus

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Normal physiology or disease?

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Signs & Symptoms of Normal Pregnancy that

may Mimic Heart Disease Signs

Peripheral edema

JVD Symptoms

Reduced exercise

tolerance

Dyspnea

Auscultation

S3 gallop

Systolic ejection murmur

Chest x-ray Change in heart position &

size

Increased vascularmarkings

EKG Nonspecific ST-T wave

changes

Axis deviation

LVH

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Other systems

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Other urinary tract changes

Ureteral dilation / hydroureter

Smooth muscle relaxation

Later exacerbation by uterine obstruction

Urinary stasis*

Dilation of pelves and calyces

Increased kidney size

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Lungs and respiration

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Respiratory Changes

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Gastrointestinal

Slowed GI motility

Constipation, early satiety

Relaxation of LES GERD

Nausea / vomiting

Often proportional to HCG level

Liver / gallbladder Biliary stasis, cholesterol saturation

More stones

Coagulation factors

Increased binding proteins (thyroid, steroid, vitamin D)

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Other Endocrine

Pancreas

Carbohydrate metabolism -Insulin resistance Human placental lactogen, cortisol

Thyroid Function

Increased TIBG (via liver)

Increased total T4 and T3 free levels unchanged

HCG suppresses TSH

Adrenal function

Free plasma cortisol is elevated

CRH from placenta stimulates ACTH

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